The overall objectives of this proposal are to develop an understanding of the structure and functions of the receptor for interferon gamma (IFN- gamma) and the components coupling the receptor to its biological actions. Knowledge of its structure and transducing elements may ultimately permit targeting (activating or deactivating) the receptors or by-passing them will small non-protein molecules. The following represent specific aims: 1. Determination of the specific regions of the extracellular domain required for interaction with IFN-gamma. This will be accomplished by site-specific mutations (substitutions, deletions, insertions) of the IFN- gamma receptor to delineate the amino acid residues of the receptor interacting with the ligand. 2. Detailed analysis of the intracellular domain to elucidate the requirements for biological function of the receptor. Site-specific mutations will be used to define these. 3. Identification and cloning of the accessory factors (AF) essential for biological function of the IFN-gamma receptor. AF1, encoded by human chromosome 21, will be the first target for cloning. Other accessory factors required for antiviral activity and other actions of IFN-gamma will be identified, defined genetically through the use of somatic cell hybrids, and then cloned if possible. 4. The genes for the human and mouse IFN-gamma receptors will be characterized and their regulation studied. Ligation of the promoter of the gene to a reporter system will provide insight into the normal regulation of the gene. 5. Expression of receptors and accessory factors in Escherichia coli to provide a simple system for study of receptor ligand interactions and to provide the materials from which to generate monoclonal antibodies. 6. IFN-gamma receptors: role in differentiation, development and disease. Antibodies to the receptors and DNA probes to their sequences will be used to study directly their modulation under various physiological and pathological circumstances. Since IFN-gamma and other interferons are in use as therapeutic agents for the treatment of malignancy and other diseases, it is essential to understand how these molecules interact with cells. Knowledge of these interactions should expedite its therapeutic uses and provide a basis for developing improved strategies for treatment of diseases with IFN-gamma alone or in combination with other agents.